the movement of charged particles in a magnetic field
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The Movement of Charged Particles in a Magnetic Field. By Emily Nash And Harrison Gray. Preview. Magnetic fields and how they are created Magnetic field of the earth Solar wind and how the earth’s magnetic field affects it

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  • Magnetic fields and how they are created
  • Magnetic field of the earth
  • Solar wind and how the earth’s magnetic field affects it
  • Taking a look at the force that magnetic fields exert upon electrons by using a cathode ray tube, magnets, and some simple math.

Magnetic Fields

Magnetic Fields are created by moving

charged particles, and only affect moving

charged particles.

Forces between two electric currents is what causes a magnetic force. Two parallel currents flowing in the same direction attract each other, while two parallel currents flowing in opposite directions repel each other.


When there exists a steady

stream of electrons, a negatively charged particle, an electric

current forms, which produces

a magnetic field.

This force leads to the idea of the north and south poles of a magnetic field.



Creating a Magnetic Field

It is possible to create a magnetic field by producing an electric current, or vice versa.

When current passes through a coil of wire, it

generates a magnetic field along the access of the coil.

This is called electromagnetism



Earth\'s Magnetic Field

The Earth itself is a magnet, with a magnetic north

pole and south pole.

The origin of the Earth’s magnetic field is said to be a result of the dynamo effect, electric currents produced by the rotation of the iron-nickel core.



The Earth’s magnetic field continually traps moving charged particles coming from the sun, called solar wind.

High concentrations of these particles within the field are called the Van Allen Radiation belts.


Solar Wind


Solar Wind consists of gases comprised of protons, electrons, and ions which hurl towards the earth from the sun at velocities of 450 km/sec or higher.

Bow Shock


The path of these particles change almost directly as they hit the earth’s magnetosphere at the region called the bow shock.

The impact of the solar wind causes

The field lines facing the sun to compress,

While the field lines on the other side stream back to form a


Because the charged particles of the rays are deflected around the magnetosheath,

the earth is protected from most of the deadly radiation.


Solar Wind Cntd

Some solar wind particles, however, do escape the earth’s magnetosphere and

contribute to the Van Allen radiation belts.

  • When these particles do enter the magnetic field, they go through three motions:
  • Spiral- the particle takes a spiraling motion around a magnetic field line.
  • Bounce- the particles eventually bounce towards the opposite pole, where they spiral again.
  • Drift- as the particle continually spirals and bounces, it drift around the magnetic field and is trapped in the magnetosphere.

In order to better understand the motion of particles through a magnetic field,

we have conducted an experiment involving creating an electron beam and running it through magnets as a parallel to solar wind entering the earth’s magnetic field.


Cathode Ray Tube Cntd.

Since change in energy is the voltage times the charge

then ½mv²=qV

Therefore v= √(2qV/m)

The potential energy

of electrons is converted

to kinetic energy

Electrons are attracted to positively charged

plate. They accelerate towards it and small

percentage escape the plate through small

hole, creating electron beam.

120 Volts

Plate is heated and

electrons boil off.

Velocity= 0

Potential Energy= ½ mv^2

6.3 Volts


Calculating the Velocity of the Electrons

We now know that v= √(2qV/m), so we can now easily find the

velocity of our beam of electrons.

q(charge) of an electron= -1.6•10^-19


m(mass) of an electron=9.11•10^-31 kg




v=649•10^6 m/s



Electron Beams

In order to predict

the angle at which

the electrons are

deflected, we must

first measure

the force that the

magnetic field inserts

upon the beam

To do this, we use the equation:


Like Solar Wind,

the electrons in the

CRT beam are deflected

when entering a

magnetic field,

therefore the electron

beam “bends.”

Magnetic field

The force is always

Perpendicular to the magnetic field

And the velocity of the electrons



Calculating the Strength of the Magnetic Field

In order to find the force of the magnetic field, we must first calculate its strenghth.

Since F=qvB and, according to Newton’s second law, F=m•v²/r, we can deduce that




mass= 9.11•10^-31 kg

velocity= 6.492•10^6 m/s

Charge= 1.6•10^-19 C

And we measured the distance of the electron beam from the magnets

to be .075 meters

Therefore B= (9.11•10^-31)(6.492•10^6)/(1.6•10^-19)(.075)

B=2.772•10^-6 tesla


Calculating the Force of the Magnetic Field

Now that we know the strength of the magnetic field at the electron beam, we can

Calculate the force which the field exerts upon the electrons.



F=2.879•10^-18 N

  • Basics of Magnetic fields and electromagnetism
  • The earth’s magnetic field and how it shields the earth from solar wind
  • The movement of charged particles such as solar wind as they enter a magnetic field
  • How to find the force that magnetic field exerts upon charged particles and the strength of the field itself.
  • How to predict the path of a charged particle through a magnetic field